1. Field of the Invention
The present invention relates to an image sensor and, more particularly, to an image sensor for detecting light and an optical pointing system using the same.
2. Description of the Related Art
A conventional image sensor is configured with an N×N pixel array and obtains a two-dimensional image of a subject. Each pixel of the array generates an analog signal having a voltage corresponding to the brightness of a corresponding image area, and the image sensor outputs N2 number of analog signals generated by each pixel.
FIG. 1 is a block diagram showing the internal structure of a conventional optical pointing system with an image sensor. The optical pointing system includes an image sensor 1, an analog/digital (A/D) converter 2, a pre-filter 3, an image processor 4 and a shutter control circuit 5.
The image sensor 1 obtains a two-dimensional image of a subject and generates and outputs N2 number of output signals having analog voltage values corresponding to the brightness of each area of the obtained image.
The A/D converter 2 converts each of the signals output from the image sensor 1 into a digital signal having an n-bit structure, i.e., into an “n-bit digital signal”, and the pre-filter 3 converts each of the converted n-bit digital signals output from the A/D converter 2 into a digital signal having a 1-bit structure, i.e., into a “1-bit digital signal”.
The image processor 4 detects an image of the subject using the 1-bit digital signals converted by the pre-filter 3, compares the detected current image of the subject and the detected previous image of the subject, calculates a movement value V(K), and outputs the calculated movement value V(K).
In response to the n-bit digital signals output from the A/D converter 2, the shutter control circuit 5 generates a shutter control signal CSH and provides it to the image sensor 1.
The shutter control signal CSH controls an exposure time of the image sensor 1 so that light incident on the image sensor 1 maintains a given average value at all times, thus allowing the image sensor 1 to obtain an exact image of the subject.
In this way, the conventional optical pointing system minimizes the number of bits of data needed to calculate the movement value and provides the result to the image processor, so that it may have a fast response characteristic.
However, the conventional optical pointing system must include the A/D converter and the pre-filter in order to provide the minimized 1-bit digital signal to the image processor. Thus, its layout increases in proportion to the areas of the A/D converter and the pre-filter. In other words, when the conventional optical pointing system is implemented as a semiconductor integrated circuit, the A/D converter and the pre-filter increase chip size.